Lose isn't a short o - short o is like the o in hop.
Both loose and lose use the same o sound, that's the trouble with English phonics, one sound can have multiple spellings. In this case it's spelt as /oo/ or /oe/ but you can also spell this sound /ue/ as in prune, or /ou/ as in Lou (can't think of a better example!) or /ui/ as in bruise.
The difference in this case is the s which either makes the sound /s/ as in snake or /z/. The other problem with British phonics - one spelling can make several sounds.
Other languages don't seem to have this as much and they get bemused at the idea of poor spelling or the idea that poor spelling means a person is "thick".
Passed and past
Past is an adjective or noun, a descriptive word for a tense describing things that have happened. In the past / past times / that was a past boyfriend. You can also use it as preposition (word denoting place/direction e.g. I'm driving past a castle, or go past the Three Lions pub.
Passed is the past tense and past participle of the verb to pass, so for example
"Please pass the salt" "I passed the salt to him"
"Pass the car when you have good visibility" "I passed the car on the straight road"
"Good luck, I'm sure you'll pass the exam" "Hooray, I passed!"
"Have you seen a sign for London yet?" "We passed that hours ago!"
I think the preposition and the verb meaning that you're moving next to something and then away from it are the ones people mix up - in that case if there is another verb before it e.g. walk, drive, go, then use past. If pass is the verb, then use passed.
I'm going past / I'll drive past / I walked past ... the station
I passed the station ages ago (no other verb)